\documentclass{beamer}
\setbeamertemplate{navigation symbols}{} % Has anyone ever used these?
\begin{document}
\begin{frame}
	\begin{tabular}{|l|r||l|r|}
		\hline
		\multicolumn{2}{|c||}{\onslide<2->{\textsc{Actif}}} & \multicolumn{2}{c|}{\onslide<2->{ \textsc{Passif}}} \\
		\hline
		\hline
		\onslide<3->{Banque}         & \onslide<3->{18550}  & \onslide<4->{Capital}        & \onslide<4->{18550}  \\
		\hline
		\onslide<5->{\textbf{Total}} & \onslide<5->{18550}  & \onslide<5->{\textbf{Total}} & \onslide<5->{18550}  \\
		\hline
	\end{tabular}
\end{frame}
\end{document}
